A major deficiency of most existing air conditioning systems is their inability to remove high levels of humidity such as those associated with the significant quantities of outside air that are required by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) standards (mandatory in the U.S.) and for health reasons. A number of desiccant systems have been tried in order to solve this problem economically but none has achieved high market penetration.
The energy used in buildings for heating and cooling comprises more than 30% of all energy used in the USA. Much of this energy is from fossil fuel sources, and the level of usage of fossil fuels is currently causing much concern. In particular, air conditioning is almost entirely powered by electricity, most of which is from fossil fuels. Electricity used for air conditioning also contributes to a large peak of electrical consumption that requires a high level of expensive peak power generation plant capacity. It would therefore be desirable if air conditioning were much more efficient in its use of electric power or were powered by non-electric or non-fossil fuel sources.
Air conditioning by compressors can remove only a fraction of the humidity from the air in humid climates. This leads to a provision of excess capacity and low refrigeration temperatures for humidity removal and the need to re-heat the air supplied to buildings. Both of these factors require considerable power usage and energy wastage. U.S. Department of Energy sources indicate that this could be as high as 60% of energy used in air conditioning. A large quantity (about 31% globally) of primary energy supplied results in waste heat that could be collected and used for low temperature energy use such as the air conditioner described below.
Desiccant-based dehumidifiers and air conditioners have been introduced to the market on a number of occasions over the past 75 years but they have not been well received for a number of reasons. Firstly, they have been expensive to buy and any energy savings from their use have not been sufficient to pay back the capital cost on a time-scale considered economic to most building owners and operators. Secondly, some liquid desiccant systems were prone to allow droplets of the liquid desiccant to carry over into the conditioned space, which is highly undesirable.
U.S. Pat. No. 5,123,481 to Albers et al. describes a process of air-cooling and dehumidification. In U.S. Pat. No. 5,123,481, Albers, et al. use sectors in an air stream and partitions or heat exchangers to transfer the heat to an airstream in a second chamber in which water is evaporated as a heat sink.
U.S. Pat. Nos. 4,982,782, 5,020,335 and 5,020,588, also to Albers et al., use a heat connecting partition and a plurality of gas streams.
Lowenstein U.S. Pat. No. 5,351,497 uses a low flow desiccant system that does not use turbulent heat exchange nor multiple sectors.
Hargis U.S. Pat. No. 8,268,060 B2 discloses a device using liquid desiccant and a compressor and heat exchangers. Hargis splits the desiccant streams into two components only one of which is passed through a heat exchanger. Thus Hargis is exposing the air streams to two (or more) desiccant stages that are at different temperatures rather than different relative humidities. Hargis also regenerates the desiccant using an outside airstream rather than the drier exhaust air from the building.
Forkosh has U.S. Pat. Nos. 6,487,872, 6,494,053, 6,575,228 and 6,976,365 that use a liquid desiccant and usually a compressor to provide the heat sink and source. Forkosh uses a single sump in either the dehumidifier or regenerator and the desiccant therefore mixes to a single concentration. Thus the “stages” described by Forkosh do not enable the separation of the desiccant into differing concentrations.
Albers and Yuan filed application US 2005/0109052 A1 for a device using a compressor and liquid desiccant. Although that device had distinct sectors, it was not arranged for separate heat input and output in each of these sectors. The heat transfer from the heat source (compressor) to the heat and mass transfer substance (desiccant) takes place at only one of the sectors, and the objective of the method is stated to be to induce a “temperature gradient” in the desiccant between the sectors rather than a concentration gradient.
There is a need for a dehumidification and/or air conditioning device that enables the use of lower temperature regeneration heat sources and less-cold cooling sources.